commit 00aabcfe3254950360e2940027950d862221ff35 Author: Richard Dodd Date: Mon Oct 23 13:14:24 2017 +0100 First commit diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..6aa1064 --- /dev/null +++ b/.gitignore @@ -0,0 +1,3 @@ +/target/ +**/*.rs.bk +Cargo.lock diff --git a/Cargo.toml b/Cargo.toml new file mode 100644 index 0000000..a3a4b41 --- /dev/null +++ b/Cargo.toml @@ -0,0 +1,13 @@ +[package] +name = "integer-sqrt" +description = """ +An implementation of integer square root algorithm for primitive rust types""" +version = "0.1.0" +authors = ["Richard Dodd "] +include = ["src/**/*.rs", "Cargo.toml"] +repository = "https://github.com/derekdreery/integer-sqrt-rs" +readme = "README.md" +keywords = ["integer", "square", "root", "isqrt", "sqrt"] +categories = ["algorithms", "no-std"] +license = "Apache-2.0/MIT" + diff --git a/LICENSE-APACHE b/LICENSE-APACHE new file mode 100644 index 0000000..8dada3e --- /dev/null +++ b/LICENSE-APACHE @@ -0,0 +1,201 @@ + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. 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IN NO EVENT SHALL THE +AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE +SOFTWARE. diff --git a/README.md b/README.md new file mode 100644 index 0000000..0623748 --- /dev/null +++ b/README.md @@ -0,0 +1,17 @@ + +# Integer square root + +This module contains the single trait `IntegerSquareRoot` and implements it +for primitive integer types. + +## Example + +```rust +extern crate integer_sqrt; + +// `use` trait to get functionality +use integer_sqrt::IntegerSquareRoot; + +assert_eq!(4u8.integer_sqrt(), 2); +``` + diff --git a/src/lib.rs b/src/lib.rs new file mode 100644 index 0000000..48f18c3 --- /dev/null +++ b/src/lib.rs @@ -0,0 +1,165 @@ +//! +//! This module contains the single trait [`IntegerSquareRoot`] and implements it for primitive +//! integer types. +//! +//! # Example +//! +//! ``` +//! extern crate integer_sqrt; +//! // `use` trait to get functionality +//! use integer_sqrt::IntegerSquareRoot; +//! +//! # fn main() { +//! assert_eq!(4u8.integer_sqrt(), 2); +//! ``` +//! +//! [`IntegerSquareRoot`]: ./trait.IntegerSquareRoot.html + +/// A trait implementing integer square root. +pub trait IntegerSquareRoot { + /// Find the integer square root. + /// + /// See [Integer_square_root on wikipedia][wiki_article] for more information (and also the + /// source of this algorithm) + /// + /// # Panics + /// + /// For negative numbers (`i` family) this function will panic on negative input + /// + /// [wiki_article]: https://en.wikipedia.org/wiki/Integer_square_root + fn integer_sqrt(&self) -> Self where Self: Sized { + self.integer_sqrt_checked().expect("cannot calculate square root of negative number") + } + + /// Find the integer square root, returning `None` if the number is negative (this can never + /// happen for unsigned types). + fn integer_sqrt_checked(&self) -> Option where Self: Sized; +} + +// This could be more optimized +macro_rules! impl_isqrt { + () => (); + ($t:ty) => {impl_isqrt!($t,);}; + ($t:ty, $($e:tt)*) => { + impl IntegerSquareRoot for $t { + #[allow(unused_comparisons)] + fn integer_sqrt_checked(&self) -> Option { + // Hopefully this will be stripped for unsigned numbers (impossible condition) + if *self < 0 { + return None + } + // Find greatest shift + let mut shift = 2; + let mut n_shifted = *self >> shift; + // We check for n_shifted being self, since some implementations of logical + // right shifting shift modulo the word size. + while n_shifted != 0 && n_shifted != *self { + shift = shift + 2; + n_shifted = self.wrapping_shr(shift); + } + shift = shift - 2; + + // Find digits of result. + let mut result = 0; + loop { + result = result << 1; + let candidate_result = result + 1; + if candidate_result * candidate_result <= *self >> shift { + result = candidate_result; + } + if shift == 0 { + break; + } + shift = shift.saturating_sub(2); + } + + Some(result) + } + } + + impl_isqrt!($($e)*); + }; +} + + +impl_isqrt!(usize, u64, u32, u16, u8, isize, i64, i32, i16, i8); + + +#[cfg(test)] +mod tests { + use super::IntegerSquareRoot; + use std::{u8, u16, u64, i8}; + + #[test] + fn u8_sqrt() { + let tests = [ + (0u8, 0u8), + (4, 2), + (7, 2), + (81, 9), + (80, 8), + (u8::MAX, (u8::MAX as f64).sqrt() as u8), + ]; + for &(in_, out) in tests.iter() { + assert_eq!(in_.integer_sqrt(), out, "in {}", in_); + } + } + + #[test] + fn i8_sqrt() { + let tests = [ + (0i8, 0i8), + (4, 2), + (7, 2), + (81, 9), + (80, 8), + (i8::MAX, (i8::MAX as f64).sqrt() as i8), + ]; + for &(in_, out) in tests.iter() { + assert_eq!(in_.integer_sqrt(), out, "in {}", in_); + } + } + + #[test] + #[should_panic] + fn i8_sqrt_negative() { + (-12i8).integer_sqrt(); + } + + #[test] + fn u16_sqrt() { + let tests = [ + (0u16, 0u16), + (4, 2), + (7, 2), + (81, 9), + (80, 8), + (u16::MAX, (u16::MAX as f64).sqrt() as u16), + ]; + for &(in_, out) in tests.iter() { + assert_eq!(in_.integer_sqrt(), out, "in {}", in_); + } + } + + #[test] + fn u64_sqrt() { + let sqrt_max = 4_294_967_295; + let tests = [ + (0u64, 0u64), + (4, 2), + (7, 2), + (81, 9), + (80, 8), + (u64::MAX, sqrt_max), + ]; + for &(in_, out) in tests.iter() { + assert_eq!(in_.integer_sqrt(), out, "in {}", in_); + } + // checks to make sure we have the right number for u64::MAX.integer_sqrt() + // we can't use the same strategy as in previous tests as f64 is now not returning the + // correct floored integer + assert!(sqrt_max * sqrt_max <= u64::MAX); + // check that the next number's square overflows + assert!((sqrt_max + 1).checked_mul(sqrt_max + 1).is_none()); + } +}